1. Field of the Invention
This invention relates to needleless hypodermic medicators for effecting subcutaneous and intramuscular injections of medicaments and the like into animate or inanimate bodies. More specifically, the invention relates to an improved medicator of the type wherein a high pressure, explosive actuated plunger is utilized to discharge a material quantity of injectant fluid from a disposable ampule.
2. Prior Art
Techniques have evolved for subcutaneous innoculations or other injections without the use of a hypodermic needle in which a metered dose of injectant is projected against the skin at such high pressures and velocity that it penetrates the skin. Typically in such apparatus gas is released at very high pressure from a suitable propellant charge, the gas operating a piston or plunger for generating the requisite pressure used to eject the medicament or the like through a fine orifice. The high pressure exerted ejects the medicament in a very fine stream or jet at high velocity, the kinetic energy of which causes the stream to enter the body.
Among this type of prior art devices are those adapted to be fitted with a unitary disposable ampule which contains a quantity of the selected medicament and is provided with a suitable explosive charge at one end, an orifice at its other end and the explosive actuated piston or plunger situated between the charge and the medicament. Under the impulse of combustion of the charge, the piston is forced down the ampule to expel the medicament from the orifice. Detonation of the charge is effected by a discrete reusable actuating unit containing a triggering and firing mechanism. The actuating unit also comprises a housing portion, typically in the form of a barrel, formed to receive the ampule. Such an injection system utilizing a reusable actuated unit for use with a disposable medicant or ampule of the type discussed hereintofore is, for example, disclosed in our co-pending patent application Ser. No. 730,421 filed 7 October 1976 and entitled "PYROTECHNICALLY POWERED NEEDLELESS INJECTOR."
With direct explosive actuation in a closed system where both the medicament and the explosive are loaded in the same capsule or ampule and where the explosively actuated force is generated and applied directly into the piston to expel the medicament from the orifice in the capsule, there has always been the danger of mutual contamination. Prior art attempts to prevent such contamination have not been fully effective, or have been commercially infeasible. To protect the medicament from any gas penetration upon combustion of the propellant charge, it has been proposed in the aforementioned copending application to provide one or a plurality of sealing O-ring members around the piston body. Although the provision of such a sealing arrangement for this type of directly actuated medicator has proved to be satisfactory in most instances, the high peak pressures, pressure surges and rapid pressure fluctuations inherent with this type of injector system, still tend to affect the overall sealing efficiency of the device.
The principal object of the subject invention is to provide a pyrotechnically charged needleless hypodermic injector having novel sealing structure enabling the device to maintain uniform sealing efficiency over a wide range of pressures.